1. Technical Field
The present invention relates to an ultrasound diagnostic apparatus for forming display images of an object in periodic motion.
2. Related Art
Ultrasound diagnostic apparatuses for forming three-dimensional ultrasound images of tissue in motion, such as a heart, have been known. For example, in a known technique, ultrasonic beams are scanned in a three-dimensional region to acquire echo data from the three-dimensional region, and, based on the acquired echo data, a three-dimensional ultrasound image is formed, to be displayed in real time. However, real-time display has a fundamental constraint in that a tradeoff relationship exists among scan rate, beam density, and beam range.
A technique for preventing the fundamental constraint in real-time display of three-dimensional ultrasound images has also been proposed. For example, JP 3537594B (Patent Document 1) discloses a technique in which a scanning plane is gradually displaced within the three-dimensional region in synchronization with electrocardiographic signals or the like; a plurality of sets of tomographic image data are acquired over a plurality of time phases at respective positions of the scanning planes; and the plurality of sets of acquired tomographic image data are rearranged and reconstructed to form three-dimensional image data (a reconfiguration process or reconstruction process). However, difficulty is encountered in applying this technique to, for example, a fetus, from which electrocardiographic signals may not be obtained directly.
JP 2005-74225 A (Patent Document 2) discloses a technique for reconstruction by performing scanning at certain time intervals, rather than using electrocardiographic signals. However, in this technique, the motion period of an object such as a heart during data acquisition is assumed to be constant. If the motion period of a heart is not constant, the form of the heart in the reconstructed image may be distorted from the actual form of the heart, thereby lowering reliability.
In view of the above-described related art, the inventor of the present invention has performed research and development for a technique of forming ultrasound images by means of a reconfiguration process. In particular, the inventor has performed research and development on a reconfiguration process preferable for an object in a motion having an unstable period.